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414Lecture8preview - Lecture 8 Transport Layer Selective...

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Lecture 8 Transport Layer Selective Repeat, TCP ECSE 414 – Fall 2010
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ECSE 414, Lecture 8 2 Announcements Project description due this Thursday, Sep 30 Homework Assignment #2 Due Tuesday, October 13 2010 Michael Rabbat
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ECSE 414, Lecture 8 3 Reliable Data Transfer Stop-and-wait: one packet in flight is inefficient Pipelining Send multiple packets in parallel Need more sequence number bits Sender/receiver needs to buffer Go-Back-N – a pipelined protocol Up to N packets in flight (window size) Sender buffers and retransmits all up to base on timeout Cumulative acknowledgments No buffer at receiver Today: Selective Repeat – another pipelined protocol 2010 Michael Rabbat
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ECSE 414, Lecture 8 4 Selective Repeat receiver individually acknowledges all correctly received packets buffers packets, as needed, for eventual in-order delivery to upper layer sender only resends packets for which ACK not received sender timer for each unACKed pkt sender window N consecutive seq #’s again limits seq #s of sent, unACKed packets 2010 Michael Rabbat
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ECSE 414, Lecture 8 5 Selective repeat data from above : if next available seq # in window, send packet timeout(n): resend packet n, restart timer ACK(n) in [sendbase,sendbase+N]: mark packet n as received if n smallest unACKed packet, advance window base to next unACKed seq # sender packet n in [rcvbase, rcvbase+N-1] send ACK(n) out-of-order: buffer in-order: deliver (also deliver buffered, in-order pkts), advance window to next not- yet-received pkt packet n in [rcvbase-N,rcvbase-1] ACK(n) otherwise: ignore receiver 2010 Michael Rabbat
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ECSE 414, Lecture 8 6 Selective repeat in action 2010 Michael Rabbat
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ECSE 414, Lecture 8 7 Selective repeat: dilemma Example: seq #’s: 0, 1, 2, 3 window size=3 receiver sees no difference in two scenarios! incorrectly passes duplicate data as new in (a) Q: what relationship between seq # size and window size? 2010 Michael Rabbat
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ECSE 414, Lecture 8 8 TCP: Overview RFCs: 793, 1122, 1323, 2018, 2581 full duplex data: bi-directional data flow in same connection MSS: maximum segment size pipelined: TCP congestion and flow control set window size flow controlled: sender will not overwhelm receiver point-to-point: one sender, one receiver connection-oriented: handshaking (exchange of control msgs) reliable, in-order byte steam: no “message boundaries” 2010 Michael Rabbat
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ECSE 414, Lecture 8 9 TCP segment structure source port # dest port # 32 bits application data (variable length) sequence number acknowledgement number Receive window Urg data pnter checksum F S R P A U
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This note was uploaded on 05/09/2011 for the course ECSE 414 taught by Professor Rabbat during the Fall '10 term at McGill.

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414Lecture8preview - Lecture 8 Transport Layer Selective...

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